Mechanical damper

Abstract: The mechanical damper (70) is fabricated from a relatively thin metal spring stock and formed in cross-section to an E-shape that is arcuately bent into a ring that fits into the cavity defined between the inner diameter of the inner shroud (24) and the outer diameter of the segmented back rings (40) of the honeycomb sealing structure (30) of the stator for the compressor of a gas turbine engine. The E-shaped damper is segmented and provides damping of the compressor stator of a gas turbine engine and is particularly adapted for stators that are formed from integrally cast stator vanes (12) and shrouds (24).

Description: This invention relates to mechanical spring-type dampers and particularly to means for damping cast stators used e.g. on compressors for gas turbine engines. As is well known in the gas turbine engine art, integrally cast stator vanes and shrouds are inherently not capable of providing damping. In the interest of reducing cost in a gas turbine engine, it is desirable to utilize cast parts whenever and wherever practical. The compressor stators and particularly the stators used on the high pressure compressor have proven to be likely candidates where cast parts can be utilized. However, as was mentioned in the above, because cast stator vanes and shrouds inherently do not have damping capabilities in comparison with other similar fabricated designs, the lack of damping has been a major obstacle standing in the way of utilizing cast parts. As is obvious to one skilled in this art and well known in this industry, damping is essential. Damping is not only necessary to withstand the exceedingly high vibratory stresses incidental in aircraft operation, it must also keep the parts out of resonance to assure their adequate life. It is therefore imperative that damping be incorporated in cast parts in order to attain the desired structural integrity needed in this environment. Another obstacle that faces the designer of aircraft engine hardware is the limited available space for incorporating dampers. Obviously, commercially available dampers are non-existent and hence unavailable. To this end, this invention contemplates a mechanical spring-like damper that is capable of providing sufficient loading required for damping the vibratory energy existing in this hostile environment and being sufficiently small to be able to fit into the limited space of the available envelope of a high pressure compressor stator of a gas turbine engine. GB-2219355 discloses using a resilient spring member as a damper which is slidable on an inner air seal and/or a stator vane. An object of this invention is to provide a damper for a cast stator for a gas turbine engine. According to the present invention, there is provided the combination as claimed in claims 1 and 2. A feature of this invention is to provide a spring-like damper that is fabricated from a highly resilient, flexible preferably metallic spring material which is shaped in the form of an "E" in cross-section. Another feature of this invention is to provide an annular E-shaped spring damper (either segmented or continuous) that is sufficiently small to fit into a cavity located on the inside diameter of the shroud of the stator and retained by the honeycomb ring segments circumferentially disposed about the stator. The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings which show an embodiment of the invention by way of example only. Fig. 1 is a partial view in section illustrating three rows of stator vanes for a compressor of a gas turbine engine incorporating this invention; Fig. 2 is a front plan view of the stator vanes taken along line 2-2 in Fig. 1; Fig. 3 is an enlarged view in section of one row of stator vanes incorporating this invention; Fig. 4 is an enlarged view in section of another row of stator vanes incorporating this invention; and Fig. 5 is an enlarged view in section of another row of stator vanes incorporating this invention where the E-shaped spring damper is disposed in a different orientation from the damper depicted in Figs. 3 and 4. While this invention in its preferred embodiment has particular utility for gas turbine engines, as one skilled in this art will appreciate, it has application in rotating machinery in other environments. Suffice it to say that this invention is particularly efficacious for damping vibratory stresses for rotating machinery where there is very little room available to accommodate dampers. As best seen in Fig. 1 which is a partial view illustrating the stator section of a high pressure compressor for a gas turbine engine, the stator section generally illustrated by reference numeral 10 comprises three (3) rows of vanes 12, 14, and 16 supported to the annular segmented outer shrouds 18, 20 and 22 respectively. An inner shroud 24, 26 and 28 respectively supports the inner diameter of the vanes 12, 14 and 16, respectively. Supported to the inner diameter of the inner shrouds 24, 26 and 28 are the annular honeycomb segments 30, 32 and 34, respectively that form the labyrinth seal used to seal the fluid medium in the gas path defined between the inner shrouds 24, 26, and 28 and the outer shrouds 18, 20 and 22. A portion of the drum rotor 36 that carries the compressor rotor blades (not shown) that are rotary mounted to extend adjacent to the respective vanes and to receive the engine working medium to be compressed is shown to illustrate the teeth 38 of the labyrinth seal and how it cooperates with the respective honeycomb segments. As this invention is only concerned with the damper aspects of the compressor stator, for the sake of convenience and simplicity the details of the compressor and gas turbine engine are omitted herefrom. For further details reference should be made to U. S. Patent Number 5,127,794. As noted in Figs. 1 and 3-5, the segmented back rings 40, 42 and 44 of the honeycomb segments serve to attach the honeycomb to the depending flanges 46 and 48, 50 and 52, and 54 and 56, respectively. Each of the segmented back rings 40, 42 and 44 are bent to define a U-shaped channel to allow the respective flanges to slide into them. Pins 58, 60 and 62, respectively, serve to secure the honeycomb elements to the inner shrouds 24, 26 and 28 in a well known manner. Depending on the particular design configuration, it is typical to include an intermediate support, such as the depending members 64, 66 and 68 to support the honeycomb as shown. What has been described in the immediate paragraphs above is the typical and well known design for compressor stators in gas turbine engines. These component parts may be fabricated or cast. As mentioned earlier, when the parts are cast, the cast parts cannot damp out the vibrations encountered. As a consequence, this vibratory energy can lead to the malfunction or destruction of the component parts of the stator. As noted in these designs, a cavity is formed between the end flange and the depending member. This invention has been able to capitalize on this envelope and utilize this cavity, notwithstanding the fact that in actuality this area provides very little space. A judiciously shaped damper is discretely located so as to provide sufficient frictional damping to attenuate the frequencies encountered in this environment. In accordance with this invention, dampers 70, 72 and 74 are formed from spring material, e.g. relatively thin metal spring stock, into E-shaped segments in cross-section that are fitted and compressed into cavities 76, 78 and 80 respectively. Each damper has a pair of end legs at its opposite ends, and between the end legs it is bent to form three generally parallel lobes giving it generally an E-shaped appearance. If the cross-section is regarded as a repeating wave shape, then there are 2½ complete waves. Each segment is bent into an arcuate shaped segment to define the annular shape to conform to the annular cavity formed on the inner diameter of the inner shrouds 24, 26 and 28. The end legs of the E-shaped damper bear against the inner surface of the respective flange and the radial extending portion of the honeycomb ring back segment that bears against the depending flange (64, 66, 68) and defines the cavity, and are compressed into the cavity of the stator. Each end leg of the damper is bent back slightly away from the end of the damper to produce a convex outer contact surface which contacts the respective flange essentially along a line. It is retained in that location by the respective inner shrouds and honeycomb ring segments which slide circumferentially around the stator. As is apparent from the foregoing, the E-shaped damper is relatively simple to make and is effective to work in confined spaces and hence requires a minimum of space. As noted above, since it is flexible in its design, as one skilled in this art will appreciate, it has potential for being utilized for other applications. Because of its shape, the spring damper has a large load variation available which makes it efficacious in the hostile environment encountered in gas turbine engines. Of noteworthiness is the fact that because the E-shaped damper has a large deflection capability, it overcomes the problem of tolerance accumulation usually encountered with cast compressor stators. FIG. 5 exemplifies how the E-shaped damper may be assembled in similar applications for compressor stators. In this configuration the "E" of the E-shaped damper is rotated 90 degrees so that the end legs of the E-shaped damper bear against the bottom surface 90 of the inner diameter of the inner shroud 28 and the outer surface 92 of the honeycomb segmented back ring 44. Identical results are obtainable in either configuration and the orientation of the E-shaped damper will depend on the particular design configuration.

Claims: In combination, a stator (10) for rotating machinery comprising: integrally cast stator vanes (12;14;16) ; an inner and outer shroud (18,24;20,26;22,28), the inner shroud (24;26;28) being disposed adjacent to the inner diameter of said stator vanes (12;14;16) and defining an annular surface; a segmented honeycomb seal element (30;32;34) concentrically supported to the inner shroud (24;26;28) and defining with said annular surface an annular cavity (76;78;80) ; and segmented back rings (40;42;44) supporting said segmented honeycomb seal element (30;32;34) and support means (46-56) to support said segmented back rings (40;42;44) to said stator; characterised in that said combination further comprises: an E-shaped mechanical damper (70;72;74) being E-shaped in cross-section and fabricated from flexible, resilient spring material adaptable to form an annular shape to fit within said annular cavity (76;78;80) and bear against the surface of said inner shroud (24;26;28) in frictional relationship to dissipate energy of the vibratory motion imparted to said stator (10); wherein the inner shroud (24;26;28) further comprises a pair of spaced radial depending walls (64;66;68) defining said annular cavity (76;78;80) of said inner shroud (24;26;28), said E-shaped mechanical damper (70;72;74) including a pair of end legs, one of said end legs bearing against one of said pair of radial depending walls; and wherein said segmented back rings (40;42;44) include a radial extending portion bearing against one of said radial depending walls (64;66;68), and the other of said end legs of said E-shaped damper (70;72;74) bears against said radial extending portion of said segmented back rings (40;42;44). In combination, a stator (10) for rotating machinery comprising: integrally cast stator vanes (12;14;16) ; an inner and outer shroud (18,24;20,26;22,28), the inner shroud (24;26;28) being disposed adjacent to the inner diameter of said stator vanes (12;14;16) and defining an annular surface; a segmented honeycomb seal element (30;32;34) concentrically supported to the inner shroud (24;26;28) and defining with said annular surface an annular cavity (76;78;80) ; and segmented back rings (40;42;44) supporting said segmented honeycomb seal element (30;32;34) and support means (46-56) to support said segmented back rings (40;42;44) to said stator; characterised in that said combination further comprises: an E-shaped mechanical damper (70;72;74) being E-shaped in cross-section and fabricated from flexible, resilient spring material adaptable to form an annular shape to fit within said annular cavity (76;78;80) and bear against the surface of said inner shroud (24;26;28) in frictional relationship to dissipate energy of the vibratory motion imparted-to said stator (10); and wherein the E-shaped damper (70;72;74) includes end legs, one of said end legs bearing against the inner surface (90) of said inner shroud (24;26;28) and the other of said end legs bearing against the outer surface (92) of said segmented back rings (40;42;44). The combination as claimed in claim 1 or 2, wherein the inner shroud (24;26;28) is disposed in the compressor of a gas turbine engine and said compressor includes a drum rotor (36) having radially extending teeth (38) that engage the honeycomb of said segmented honeycomb seal element (30;32;34) to form a seal to prevent leakage of the working fluid medium of said gas turbine engine. The combination as claimed in any preceding claim, wherein said support means (46-56) includes axially extending flanges (46-56) disposed on opposite axial sides of said inner shroud (24;26;28), and said segmented back rings (40;42;44) include complementary U-shaped side portions defining annular channels to accommodate each of said axially extending flanges (46-56). The combination of any preceding claim, wherein said E-shaped damper (70;72;74) is circumferentially segmented.

Inventors: ALVAREZ JOSE M JR, BONNER KURT J, ALVAREZ, JOSE M., JR., BONNER, KURT J.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1994
Main classification: F01D25
IPC codes: F01D11, F01D25, F16F15, F01D9